Microlenses have long been used in imaging devices to focus light on sensors including charge couple device (CCD) sensors and complementary metal oxide semiconductor (CMOS) sensors. The microlenses significantly improved the light sensitivity of the imaging device. An imaging device is typically made up of an array of sensors, each sensor having a small light sensitive collection area. The microlenses improve light sensitivity of the imaging device by collecting light from a large area and focusing it on a small light sensitive collection area. The ratio of the light sensitive collection area to the total area of the sensor is defined to be a fill factor. Typical fill factors in prior art designs are less than 50%.
Microlenses are also used in display devices. In a display device, a microlens may be used to focus light from a background light source to a switch. The area covered by the switch is substantially less than the area of the background light source. By using a microlens, the light output of the display device can be substantially increased.
Traditional microlenses were formed by flowing a microlens resist material. A positive photoresist is lithographically printed to form either a square or rectangular structure. The microlens resist is then baked at a temperature above the glass transition temperature such that the microlens resist flows and the structure "sags" resulting in a curved microlens with a radius of curvature. However, flowing of the microlens resist is a difficult process to control. The final shape of the microlens depends on variations in the material which can cause significant differences in the flow patterns of the microlens resist material. Thus, an array of microlenses subject to the same processing steps may vary in dimension. The variations make it very difficult to create arrays of microlenses with the same curvature and dimensions.
Thus an improved method of reproducing microlenses with similar characteristics is needed.